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<head>
    <meta charset="UTF-8"/>
    <title>bs401=基本使用</title>
</head>
<body>
    <ul>
        <li id="beijing" class="city">北京</li>
        <li id="shanghai">上海</li>
        <li id="shenzhen">深圳</li>
    </ul>
    <a href="https://www.baidu.com/index.htm" class="baidu">百度一下</a>
    <div id="app"><p id="lazy">哈哈啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊</p></div>
</body>
</html>